Tokkai Sho 63-219956 published by the Japanese Patent Office in 1988 discloses an infinite speed ratio transmission (referred to hereafter as IVT) which permits a speed ratio to be varied up to infinity by combining a reduction gear unit and planetary gear set with a toroidal continuously variable transmission (referred to hereafter as CVT).
The rotation of an engine is input to the CVT having a continuously variable speed ratio, and to the reduction gear unit which has a fixed speed ratio. The output shaft of the CVT is joined to a sun gear of the planetary gear set, and the rotation output of the reduction gear unit is joined to a planet carrier of the planetary gear set. A ring gear of the planetary gear set is joined to a final output shaft of the IVT. The planet carrier supports the center of plural planet gears held between the sun gear and ring gear.
An output shaft of the reduction gear unit and a planet carrier are joined via a power recirculation clutch. The output shaft of the CVT is also joined to the final output shaft via a direct clutch.
In a direct mode wherein the power recirculation clutch is disengaged and the direct clutch is engaged, the rotation of the CVT output shaft is directly output to the final output shaft, so the speed ratio li of the IVT is equal to a speed ratio lc of the CVT.
On the other hand, a power recirculation mode where the power recirculation clutch is engaged and the direct clutch is disengaged, the direction and speed of the output rotation of the final output shaft vary according to the difference between the speed ratio lc of the CVT and the speed ratio of the reduction gear unit. The speed ratio li of the IVT, i.e., the ratio of the rotation speed of the input shaft and the rotation speed of the final output shaft, varies from a negative value to a positive value. At the point where the rotation direction of the final output shaft changes, the speed ratio li of the IVT becomes infinite, and the final output shaft is stationary. This point is referred to as the geared neutral point (GNP).